Prefabricated Concrete

What is Prefabricated Concrete?: Prefabricated or Precast concrete is a construction product produced by casting concrete in a reusable mold or "form" which is then cured in a controlled environment, transported to the construction site and lifted into place. In contrast, standard concrete is poured into site-specific forms and cured on site. Precast stone is distinguished from precast concrete by using a fine aggregate in the mixture, so the final product approaches the appearance of naturally occurring rock or stone.

Advantages of Prefabricated Concrete: By producing precast concrete in a controlled environment, typically referred to as a precast plant, the precast concrete is afforded the opportunity to properly cure and be closely monitored by plant employees. Utilizing a Precast Concrete system offers many potential advantages over site casting of concrete. The production process for Precast Concrete is performed on ground level, which helps with safety throughout a project. There is a greater control of the quality of materials and workmanship in a precast plant rather than on a construction site. Financially, the forms used in a precast plant may be reused hundreds to thousands of times before they have to be replaced. This generally allows cost of formwork per unit to be lower than for site-cast production.

Types of Prefabricated Concrete:  There are many different types of precast concrete, forming systems for architectural applications, differing in size, function, and cost. Precast architectural panels are also used to clad all or part of a building facade free-standing walls used for landscaping, soundproofing, and security walls, and some can be Prestressed concrete structural elements. Stormwater drainage, water and sewage pipes, and tunnels make use of precast concrete units.

Commercial Construction Building Sequence

Sequencing of trades and tasks on a commercial construction project is vitally important to the smooth operation and completion of a project.  The Commercial Construction Project Schedule template is organized into 17 phases, depicted in the following Gantt Chart:

General conditions: The time required to finalize the plans, develop an estimate, bring the project under contract, obtain permits, begin the procurement process and the process of submitting monthly pay requests.

Long-lead procurement:      The submittal of shop drawings, approval and ultimate fabrication and delivery of the major components of a commercial building are time critical. These activities must be addressed and expedited very early in the project.

Mobilize on site: Setup of temporary utility services, field offices, lay-down areas, site parking, temporary fencing, and benchmarks.

Site grading and utilities: Clearing and grubbing the lot, installing underground utilities and site drainage systems, fire water lines, and constructing building batter boards.

Foundations: Excavation, forming, and placement of the concrete foundations, footings, piers, grade beams, elevator pits and walls, installation of anchor bolts, elevator tubes and other required activities except the forming and placement of the first floor slab, which is completed later to ensure that it isn't damaged by construction activities.

Steel erection: The erection of the steel building frame, including main and secondary members, bracing, temporary steel for construction hoists and other uses and the painting or coating of that steel.

Form and pour concrete floors and roof: Installing rebar mats and in-floor utilities and conduits, forming, placing and finishing the concrete floors and roof of the structure.

Carpentry: The rough carpentry required for installation of the building sheathing and metal lath and the construction of the basic frame of the building interior.

Masonry: The interior and exterior masonry of the building, including the elevator and utility cores, any exterior masonry, hard tile on the floors of common areas and restrooms and restroom wall tiles.

Roofing: Placement of lightweight concrete fill, installation of roof drains, flashing, polymeric or roll roofing material and coatings and the stone ballast.

Window wall and storefront closures: Installation of the metal framing and glazing components of the window walls and storefront.

Building finishes: The detailed work of completing the interior of the building. insulation, drywall, paint and paper, cabinets, millwork, carpet and tile, hardware, interior and exterior plantings, seeding and sodding, and paving / striping the parking areas. Includes all signage requirements under the building code.

Elevators: Installation of the elevator cars and controls, calibration, testing and certification of the system.

Plumbing: Rough in and final installation of service areas, restrooms, fire and irrigation systems, including piping, fixtures and controls and the effort required to obtain in-process and final inspections and acceptance.

Electrical: Rough in and final installation of service, including all non-embedded conduit, cable and fixtures, controls and services and the effort required to obtain in-process and final inspections and acceptance.

HVAC: Rough setting and final installation of environmental control systems—including equipment in mechanical spaces, roof-top units, ductwork, controls and the effort required to balance air flows and obtain in-process and final inspections and acceptance.

Final cleanup and occupancy including inspections: The effort required to achieve final inspection and certification for occupancy by the city or county building inspector, the builder's final cleanup and walkthrough with the owner, and the owner's final acceptance.

These areas are general demarcations.  Some tasks in different areas may be complimentary and, therefore, it may be appropriate for different tasks in different categories to be executed at the same time. 

Footnotes:

http://office.microsoft.com/en-us/project-help/about-the-commercial-construction-template-for-project-HA001122602.aspx

Modular Construction

Modular construction consists of buildings that are prefabricated in multiple sections called modules. The modules are constructed in a remote facility, then delivered to their intended site of use. Using a crane, the modules are set onto the building's foundation and joined together to make a single residential, or commercial, building. The modules can be placed side-by-side, end-to-end, or stacked up to 4 stories in height, allowing a wide variety of configurations and styles in the building layout.

Must Meet Code:  Modular buildings must conform to all local building codes for their proposed use. This differs from mobile homes, with which moduar construction is sometimes confused, because mobile homes are required to conform to federal codes governed by the U.S. Department of Housing and Urban Development.

Uses of Modular Buildings:  Modular buildings may be used for long-term, temporary or permanent facilities, such as construction camps, schools and classrooms, civilian and military housing, and industrial facilities. Modular buildings are used in remote and rural areas where conventional construction may not be reasonable or possible. Other uses have included churches, health care facilities, sales and retail offices, fast food restaurants and cruise ship construction.

Advantages of Modular Construction: Modular buildings are often priced lower than their site-built counterparts, for a variety of reasons. Manufacturers cite the following advantages for using modular construction: 1) Speed of construction/faster return on investment. Modular construction allows for the building and the site work to be completed simultaneously, reducing the overall completion schedule by as much as 50%; 2) Indoor construction. Assembly is independent of weather, which increases work efficiency and avoids damaged building material; 3) Favorable pricing from suppliers. Large-scale manufacturers can effectively bargain with suppliers for discounts on materials; 4) Low waste.

Project Safety

Construction is a dangerous undertaking.  Recent studies indicate that there are 400,000 reportable injuries to construction workers and more than 1.000 deaths each year in construction in the United States.  The financial impact of these construction accidents has been estimated at $2 billion.  As a result, several pieces of legislation have been implemented to address construction site safety.  Probably the most significant piece of safety legislation is the Occupational Safety and Health Act.

OSHA: The United States Occupational Safety and Health Administration (OSHA) is an agency of the United States Department of Labor. Congress established the agency under the Occupational Safety and Health Act, which President Nixon signed into law on December 29, 1970. OSHA's mission is to "assure safe and healthful working conditions for working men and women by setting and enforcing standards and by providing training, outreach, education and assistance".

The Occupational Safety and Health Act allows OSHA to issue workplace health and safety regulations. These regulations include limits on chemical exposure, employee access to information, requirements for the use of personal protective equipment, and requirements for safety procedures. Job safety posters are required to present on job sites where employees can read them.  Additionally, regular, usually weekly, safety meetings are required to occur.

Labor Law and Labor Relations

The employment of construction workers is governed by federal and state labor laws.  The requirements vary by state, but tend to be more onerous in the rust-belt and in "pro-union states" than in the South an West.  The following surveys key points of labor laws and relations.

History: Employment law in the U.S. has traditionally been governed by the common law rule of "at-will employment," meaning that an employment relationship could be terminated by either party at any time without a reason. This is still true today in most states. However, starting in 1941, a series of laws prohibited certain discriminatory firings. That is, in most states, absent an express contractual provision to the contrary, an employer can still fire an employee for no or any reason, as long as it isn't an illegal reason (which includes a violation of public policy).

Fair Employment Act: In 1941, the Fair Employment Act became the first law to prohibit racial discrimination, although it only applied to the national defense industry. 

Fair Labor Standards Act: Regulates minimum wages and overtime pay for certain employees who work more than 40 hours in a work week. While working an employee must work a minimum of two hours in a day.

National Labor Relations Act: The "Wagner Act" gives private sector workers the right to choose whether they wish to be represented by a union and establishes the National Labor Relations Board (NLRB) to hold elections for that purpose. As originally enacted in 1935, the NLRA makes it illegal for employers to discriminate against workers because of their union membership or retaliate against them for engaging in organizing campaigns or other "concerted activities", to form "company unions", or to refuse to engage in collective bargaining with the union that represents their employees.

Taft-Hartley Act: The "Labor-Management Relations Act"), passed in 1947, loosened some of the restrictions on employers, changed NLRB election procedures, and added a number of new limitations on unions. The Act, among other things, prohibits jurisdictional strikes and secondary boycotts by unions, and authorizes individual states to pass "right-to-work laws", regulates pension and other benefit plans established by unions and provides that federal courts have jurisdiction to enforce collective bargaining agreements.

Norris-LaGuardia Act: Passed in 1932 this law outlawed the issuance of injunctions in labor disputes by federal courts. While the Act does not prevent state courts from issuing injunctions, it ended what some observers called "government by injunction," in which the federal courts used injunctions to prevent unions from striking, organizing and, in some cases, even talking to workers or entering certain parts of a state. Roughly half the states have enacted their own version of the Norris-LaGuardia Act.

Project Cost Management

Project cost and its control are important managment duties.  During construction, the project cost management system retrieves costs, labor and equipment hours, and production quantities from the job site as work progresses.  The information is used  as the basis for projections for future project work and to ensure ongoing project costs remain within the project's established budget.

Construction Cost Control: Many types of construction cost controls exist.  Some of the more common techniques include: 1) Performing an adequate constructability review to minimize unexpected costs; 2) Establishing a construction cost cash flow plan; 3) Monitoring cost performance to detect and understand variances from plan; and, 4) Ensuring that all appropriate changes are recorded accurately in the cost baseline.  Cost control methods are most successful when executed at regular intervals, whether daily, weekly, monthly, etc.  The snap-shot data obtained at these regular intervals can be compared to pre-construction budget estimates and adjustments can be made, as needed, to keep the project on budget.



Value Engineering to Reduce Costs: Reducing costs without compromising value is a regular goal of owners.  Value Engineering is an organized approach to providing the necessary functions at the lowest cost -- without sacrificing quality or value. Value engineering requirements and guidelines may originate in the project contracts or may be suggested by the contractor.  Regardless of the genesis on any given project, value engineering is a great cost management/reduction tool.  

Project Time Management

Time is a crucial component of construction project managment.  In certan instances the early completion of a project can financially benefit the contractor.  Conversely, late project completion can lead to financial penalties.  Timeliness is also an important component of a contractor's reputation in the industry and may affect the contractor's ability to obtain work on future projects.  A typical construction project involves many mutually dependent and interrelated operations that, in total combination, constitute a web of individual time and sequential relationships.  When task requirements for materials, equipment, and labor are considered, the complexity of the process of planning and scheduling that is necessary for successful project time managment becomes clear.

Critical Path Method (CPM): CPM is a project management system that offers a basis for informed decision making on construction projects of any size.  It provides information necessary for the time scheduling of a project, guides the contractor in selecting the best way to shorten the project duration, and predicts manpower and equipment requirements.

     Critical path scheduling assumes that a project has been divided into activities of fixed duration and well defined predecessor relationships. A predecessor relationship implies that one activity must come before another in the schedule. No resource constraints other than those implied by precedence relationships are recognized in the simplest form of critical path scheduling. To use critical path scheduling in practice, construction planners often represent a resource constraint by a precedence relation. A resource constraint is a constraint deriving from the limited availability of some resource of equipment, material, space or labor. For example, one of two activities requiring the same piece of equipment might be arbitrarily assumed to precede the other activity. This artificial precedence constraint insures that the two activities requiring the same resource will not be scheduled at the same time. These restrictions imply that the construction plan can be represented by a network plan in which activities appear in a network, and no two activities can have the same number or designation.